While the principles of wobble centrifuge operation will be apparent from the aforedescribed copending application, the literature in the file thereof and from the commonly assigned prior U.S. Pat. No. 4,153,551 issued May 8, 1979 (and the publications there cited), a brief review of these principles may assist in a similar understanding of the present invention.
In a wobble centrifuge, especially for the continuous operation of a liquid from a solid in a suspension or slurry introduced into the centrifuge drum, the latter is an open-work structure which frustoconically widens toward the solids-discharge end of the drum. The mixture of liquid and solids is introduced into the interior of the drum, e.g. via a distributor, so that the solids tend to lie along the perforate inner wall of the drum while the liquid phase is forced through the openings and thereby separated by the action of centrifugal force, from the solid phase.
Since such drums are generally rotated with extremely high G forces and angular velocities, the friction between the solid phase and the inner surface of the drum may be sufficient to prevent the solids from being continuously discharged.
In a wobble centrifuge, the drum is rotated about its axis of symmetry, being a body of revolution centered therealong, with the drum surface having generatrices inclined to this axis. The drum axis, in turn, is caused to orbit a vertical axis, for example, in a gyrating or wobbling movement which imparts a slinging type of movement to the solids and thereby promotes their migration toward the discharge edge of the drum and from this edge into a collecting chamber, trough, or space. The gyrating or wobble movement is carefully controlled or established so that a continuous discharge of the solids is ensured.
The drum of such centrifuge may be made up of a grate-like arrangement of rods which extend along the generatrices of the drum and define between them slot-like gaps forming the openings in the drum through which the liquid phase is discharged.
It is known, with such grate-like drums, to provide a support structure for the rods, generally located along the structure of the drum, which can include spaced-apart rings surrounding the array of rods and bars which connect these rings and which lie in axial planes of the drum, i.e. along generatrices thereof, usually in angularly equispaced relationship. The support structure may be connected to upper and lower (end) flanges at one of which the drum is mounted for rotation about its axis on a shaft which, in turn, can be coaxial with another shaft defining the vertical or fixed axis about which the drum axis is orbited. The shaft stub which rotatably entrains the drum flange may be connected to a drive shaft by a universal joint so that the two coaxial members can be rotated at different angular velocities to establish the gyrating or precession movement.
With such wobble centrifuges, problems have been encountered which interfere with continuous operation. For example, when the solid phase includes hard, sharp-edged or elastic, ball-shaped particles, frequently these particles tend to become wedged in the gaps or slots formed between the rods so that the gaps become blocked and the efficiency of liquid separation is reduced.
Until now it has been assumed that the most effective way to overcome this disadvantage has been to properly shape the gap. For example, the cross section of the gap can increase outwardly to limit the wedge action. Notwithstanding such design techniques, however, the problem has not been completely alleviated and it has been found that this approach only reduces the magnitude of the problem.
As a result, the drums of prior art wobble centrifuges of the aforedescribed type remain susceptible to blockage.
Such blockage, naturally, reduces the separation efficiency and the degree of liquid removal so that the liquid content of the collected solid phase may increase with time until it is no longer tolerable. When blockage is acute, the apparatus must be brought to standstill, frequently interrupting a processing line at considerable cost and interruption in processing until the drum is cleared by hand.